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Las kimberlitas revelan la evolución de 2,5 mil millones de años de un depósito profundo y aislado del manto
Jon Woodhead1, Janet Hergt2, Andrea Giuliani2,3,4
1School of Earth Sciences, University of Melbourne, Melbourne, Victoria, Australia. jdwood@unimelb.edu.au.
Nature
|September 27, 2019
Resumen
Los científicos descubrieron un depósito de manto prístino de larga duración utilizando datos de kimberlita. Esta antigua fuente, aislada durante 2.500 millones de años, fue interrumpida más tarde, posiblemente por subducción, lo que explica la rareza de los derretimientos del manto primordial en la actualidad.
Área de la Ciencia:
- Geoquímica
- Ciencias de la Tierra
- Petrología
Sus antecedentes:
- La corteza continental de la Tierra se formó a partir de la extracción de la fusión del manto durante 4.500 millones de años.
- Los modelos geoquímicos y las altas proporciones de Helio-3 / Helio-4 sugieren reservorios aislados e indiferenciados del manto.
- La existencia y la longevidad de las fuentes primitivas del manto siguen siendo preguntas clave sin resolver.
Objetivo del estudio:
- Para investigar la composición y evolución del manto profundo de la Tierra utilizando kimberlitas.
- Para determinar si existe un depósito de manto prístino de larga duración y cómo evolucionó.
- Para entender la interrupción de este depósito y sus implicaciones para la dinámica del manto.
Principales métodos:
- Análisis de las proporciones de isótopos radiogénicos en kimberlitos distribuidos globalmente de diferentes edades.
- Modelado geoquímico para rastrear la evolución del manto y las características de origen.
- Mapear la distribución de las kimberlitas afectadas para inferir la naturaleza del evento de perturbación.
Principales resultados:
- Las kimberlitas se originan en un solo y homogéneo reservorio de manto prístino aislado durante al menos 2.500 millones de años.
- Este depósito estaba distribuido globalmente y es isotópicamente uniforme, lo que representa un hallazgo único.
- Hace unos 200 millones de años, este depósito fue perturbado por material exógeno, probablemente relacionado con la subducción de Pangea.
Conclusiones:
- Se ha identificado un reservorio de manto aislado de larga duración, que proporciona información sobre la historia temprana de la Tierra.
- La interrupción de este depósito sugiere un cambio significativo en los regímenes de mezcla de manto a gran escala.
- La perturbación de este antiguo depósito puede explicar la dificultad de encontrar manto primordial no contaminado en rocas volcánicas recientes.
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